Scirocco Engine Swap - Knock Sensor Installation
Installation of a high compression engine (such as 3A or ABA) into a vehicle that does not have a knock sensor requires the installation of a knock sensor.  The knock sensor protects the engine from destructive engine knock by retarding the timing upon detection of knock, and also controls timing advance.  Aftermarket options are available, but the most affordable option is to retrofit a factory knock sensor with wiring harness.

The factory VW knock sensor can be found in any CIS-E equipped VW such as the 1985 to 1988 GTI and GLI, and 1986 to 1989 16V.  Wire colors/pins may differ depending on the donor vehicle and the vehicle in which the knock sensor is being installed.  Wiring diagrams should be obtained for both vehicles to assure proper installation.

You MUST use a distributor from a vehicle originally equipped with a knock sensor.

This installation is specifically a 1985 Scirocco with 3A/JH 2.0L 8V engine, utilizing the knock sensor from a 1987 GTI.

   
Wiring Preparation
Wiring diagrams should be obtained for the donor vehicle and the vehicle in which the knock sensor is being installed. The Bentley service manuals are an excellent source for this information.   Be aware, though, that the wiring may differ slightly from the published diagrams.   Be flexible and ready for possible differences.

The following diagrams/links may be of use, but are not guaranteed for accuracy.

1986 Wiring Diagram (.pdf file)
1987 Wiring Diagram (.pdf file)
1988 Wiring Diagram (.pdf file)
Volkswagen.org Engine Swaps Thanks for everything David - VWoA and VAG can go to hell!
VW Vortex discussion on Knock Sensors (Local Copy)
TBerk's Website
 

Wiring harness preparation is fairly simple once you determine which wires are needed.
 
PIN # WIRE COLOR USE
7 Brown/White To Distributor
9 Brown/Yellow To Distributor
15 Brown/Black To Distributor
5 Yellow To power "15". Source at coil (black wire)
12 Green/White To original green/white wire going to distributor. Source at elec. ignition module.
14 Black/Red To Knock Sensor
13 Violet To Knock Sensor
10 Brown/Yellow To power "50". Source at starter
3 Brown To ground
6 Blue/White To throttle body idle switch
8 Violet To throttle body WOT switch
1   Not used (if it is present)
4   Not used (if it is present)
11   Not used (if it is present)
2 Gray/Blue Not used (if it is present)

 

Click the diagram to the right.   This will open a new window, with the diagram and chart above. Print it out for your reference. Knock Sensor Installation
This mess of wires was pulled from the donor vehicle. Only a small portion will be used, but pulling everything from the donor vehicles insures all wiring and connectors will be available.
This shows all the wiring, knock sensor, and knock sensor box. kswire1s.jpg (17967 bytes)
This is the main harness that attaches to the knock sensor box. Factory connector was left attached (bottom left). kswire2s.jpg (14963 bytes)
This part of the harness contains the wiring for the knock sensor, the wires that attached to the distributor, and the wire for power "50". The wiring harness was modified so the power "50" wire would use the factory connector. kswire3s.jpg (17026 bytes)
This part of the harness goes to the throttle body switches. The yellow wire is fused and connected directly to power "15". kswire4s.jpg (13451 bytes)
This is a Type 2 knock sensor.   Specific torque values must be used during installation to insure proper operation.

Type 1: 7-9 ft. lbs.
Type 2: 11-18 ft. lbs.

 
Installation
The wiring can be run through existing grommets to avoid drilling any holes.  If you use factory connectors, they can be disassembled and reassembled after pulling the wires through.

Disassembling the connector is as simple using a paper clip and pushing through the "wire prong" side.

Pin #12 (Green/White)
Carefully cut a small opening in the harness cover about 6" from the ignition module connector to access the green/white wire. Cut the wire and pull it out, then tape the opening.  This gives you room to work when soldering the wires.  You will connect to the wire coming from the ignition module.
Pin #5 (Yellow) and power for throttle switches
Power "15" can be sourced at the coil (black wire on back side).
Pin #10 (Brown/Yellow)
Power "50" can be sourced at the starter. A "piggyback" connector from Radio Shack made installation simple.
You will need to use the factory full throttle and idle switches from the knock sensor donor vehicle. If you did a 3A swap, these switches are on the 3A throttlebody.

This picture shows the full-throttle switch and wire connector on the Audi 3A throttlebody.

This picture shows the idle switch on the Audi 3A throttlebody.
The full-throttle and idle switches were mounted to the existing throttlebody.  (which in this case, was the larger A2 throttlebody).
 
If your car was originally equipped with a full-throttle switch, you will need to "piggyback" it with the full-throttle switch for the knock sensor.

This is easily accomplished by using longer switch mounting screws.

A vacuum line needs to be run to the knock sensor box. A "T" connector was installed near the throttlebody in the line that went to the original distributor with vacuum advance.
Bolt the knock sensor to the block.  Be sure to observe proper torque specifications.
Connect the wires to the distributor.
 
Connect PIN#3 (brown wire) to a ground. The battery is always a safe bet for grounding.
 
Double check your installation and try starting the car.  If the car cranks but does not start, the distributor timing may need advanced. 
     
Miscellaneous Observations
The car started fine before adding the knock sensor.  The distributor had not been changed.  The car would not start.  Timing had to be advanced

Prior to KS installation, the car was difficult to start when warm.  I blamed this solely on an old starter and higher compression.  The problem disappeared after installing the knock sensor.
  

Cost Overview
The price of the knock sensor box and wiring harness will vary depending on your source. 

A knock sensor costs around $50.00 - get a new one!

Miscellaneous wire connectors and heat shrink should be $10.00 to $15.00.
  

Summary
Wow!  A world of difference... lots of new found power!
 

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